DE102014112096B4 - Absorbent fibrous web - Google Patents

Abstract

A process for producing an absorbent fibrous web, which comprises the steps of a) laying fiberized cellulose fibers made of CTMP in a gas stream on a base, b) pre-compressing the cellulose fibers to produce a loose fleece, c) introducing the fleece from step b) into the gap of a Pair of calender rolls, the surfaces of the calender rolls each having projections with which the fibers from step b) are pressed together under pressure in the range between 150 to 600 MPa.

Description

The present invention relates to an absorbent fibrous web made of fibrated cellulose fibers, a process for its production and the use of this fibrous web.

Absorbent fibrous webs are used as absorbent bodies for absorbing liquids in a variety of applications, e.g. B. in food packaging, in hygiene products such as tampons, sanitary napkins, diapers and incontinence products, in medical products, such as bandages.

These absorption bodies usually consist of loosely laid fibers of natural or synthetic origin, i. H. Cellulose or cellulose fibers or plastic fibers that are compacted over their entire area or in certain areas. In order to increase the absorption capacity, so-called superabsorbent polymers are often incorporated into these absorption bodies. These superabsorbent polymers absorb liquids, especially water, and swell in the process.

In the DE 298 18 178 U1 For example, an absorbent fibrous web is disclosed which has a high absorption capacity, which can be increased by adding superabsorbents. The disclosed fibrous web consists of a high proportion of pulp fibers pressed together, which are pressed together in an embossed pattern from punctiform or line-shaped embossing areas and are fused in this embossing area free of adhesive and / or binder as a result of high pressure.

The publication DE 10 2010 006 228 A1 discloses an absorbent structure having a sequence of layers of two outer layers and a liquid storage layer disposed between the outer layers. The layers are arranged one above the other and form a layer structure. The liquid storage layer has a cellulose material, in particular cellulose fibers, and a superabsorbent polymer, in particular superabsorbent polymer particles or superabsorbent polymer fibers, and preferably no and in particular less binder than liquid storage layers of the absorbent structure adjacent to the liquid storage layer.

US2012 / 0302440 A1 discloses an absorbent article containing a freeze-dried composite material, the freeze-dried composite material containing cellulose pulp (eg CTMP) and an absorbent material, and the absorbent material containing microfibrillated cellulose (MFC) with a carboxylate group content of 0.5 to 2.2 mmol / g MFC has.

EP 0 484 101 A2 discloses a paper towel with a first layer of a chemical fiber blend and a second layer of a loose, high volume softwood fiber blend that is integral with the first layer. The first layer is made up of a chemical softwood and hardwood fiber mixture and has a higher density than the second layer and the second layer consists of about 30% to 43% loose fibers and about 57% to 70% long wood pulp fibers.

The superabsorbent materials develop their absorbency especially against water. As soon as the liquid to be absorbed contains metal ions, such as Na ⁺ or organic liquids such as ethanol, the absorbency / absorption capacity decreases sharply. With an alcohol content (ethanol) of 50% and above, no more liquid is absorbed in any significant amount. An absorption capacity is virtually no longer available.

Another disadvantage of the superabsorbent polymers is that, as an additive, they always entail additional costs, both for the material as such and for incorporation into an absorption body means an additional work step and thus higher production costs. In addition, official approvals must be applied for the use of synthetic materials such as SAP in food packaging and hygiene, while cellulose fibers can be used without such approval procedures.

The object of the present invention was to provide an absorbent fibrous material which essentially consists of cellulose fibers or cellulose fibers and has a high absorption capacity against oil, water, aqueous solutions and also ethanol and is almost independent of the metal ion concentration. For use in the hygiene and food sector, it is also important that all substances used are harmless to human toxicology. As far as possible, the use of superabsorbent polymers should be avoided.

1. a) wirres Legen von aufgefaserten Zellstofffasern aus CMTP in einem Gasstrom auf einer Unterlage,
2. b) Vorverdichten der Fasern unter Erzeugung eines lockeren Vlieses,
3. c) Einführen des Vlieses aus Schritt b) in den Spalt eines Kalanderrollenpaares, wobei die Oberflächen der Kalanderrollen jeweils Vorsprünge aufweisen, mit denen die Fasern aus Schritt b) unter Druck im Bereich zwischen 150 bis 600 MPa aufeinandergedrückt werden.

The present invention relates to a method for producing the absorbent fibrous web described above, which comprises the method steps

1. a) tangled laying of fiber pulp fibers made of CMTP in a gas stream on a base,
2. b) pre-compressing the fibers to produce a loose fleece,
3. c) inserting the fleece from step b) into the nip of a pair of calender rolls, the surfaces of the calender rolls each having projections with which the fibers from step b) are pressed onto one another under pressure in the range between 150 to 600 MPa.

An object of the present invention is therefore an absorbent fibrous web made of fiber pulp, which is characterized in that it has a free swell capacity (FSC) compared to a 0.9% NaCl solution of at least 16 g / g fibrous web and a Absorption capacity according to the BfR method of at least 6g / g.

Surprisingly, it was found that a fibrous web made from fiber pulp, even without so-called polymeric suction enhancers, such as superabsorbent polymers, has an absorption capacity, namely a so-called Free Swell Capacity (FSC), compared to a 0.9% NaCI solution of at least 16 g / g fibrous web has, whereby additives such as superabsorbent polymers, CMC, pectins or the like can be dispensed with. The so-called free swell capacity is preferably at least 20 g / g compared to a 0.9% NaCl solution and in particular at least 24 g / g, determined analogously to the Edana test method 440.2-02 or ISO 17190-5: 2,001th

The absorption performance is preferably also determined by the BfR method, i.e. under load, clearly above the values as shown in the products known from the prior art, and is preferably at least 8 g / g of fibrous web, determined in accordance with the 61st communication of the Federal Office for Risk Assessment (BfR) published in health sheet 04.2003.

The retention (CRC = Centrifuge Retention Capacity) is preferably significantly higher than that compared to the products from the prior art and is at least 1.3 g / g fibrous web, in particular at least 1.5 g / g, determined analogously to the Edana test method 441.2-02 or ISO 17190-6: 2001.

According to the invention, the absorbent fibrous web is made from fiber-pulp. Any pulp materials known from the prior art can be used as pulp materials, such as mechanical pulp (MP), TMP (thermomechanical pulp), CTMP (chemithermomechanical pulp), HT-CTMP (high temperature chemithermomechanical pulp), wood pulp and fluff pulp as well as any Mixtures of the named pulps. Particularly good results are obtained with CTMP, for example a CTMP, as described by the method in the WO 91/12367 A1 is obtained or HT-CTMP, obtainable by a method according to WO 95/34711 A1 , The pulp fibers used are preferably unpurified or partially cleaned fibers which still contain lignin and have a corresponding brightness. The brightness (analogous to Edana test method 100.1-78 (ISO 2470: 1977) is preferably over 40%, in particular at least 55% and should not exceed 85%. These fiber materials are commercially available and can be used to produce the fibrous web according to the invention in a manner known per se The fiber pulp is preferably present after the fiberization as a heaped-up bed of the cellulose fibers obtained. The bed of the cellulose fibers can be formed in a gas stream or in water or another medium, with a bedding in the air stream being preferred. Bulk density of the pulp pulp is preferably between 5 and 300 g / cm ^3, preferably 10 and 200 g / cm ³ .

For the use of the fibrous web according to the invention in food packaging or also in the medical field or for hygiene articles, it has proven suitable if the weight per unit area is between 60 and 1500 g / m ² , preferably in the range from 90 to 900 g / m ² and in particular from 120 to 700 g / m ² .

The fiber material used in step a) preferably consists of fiberized, i.e. defiberized pulp fibers. Pulp fibers are usually commercially available in the form of bales, sheets or rolls. The commercially available fiber materials can be fiberized in devices known to those skilled in the art, such as crushed in a hammer mill or other type of finder, such as a disc refiner or pin mill.

The absorbent fibrous web is produced by shaping the fiber pulp as described above in a gas stream, in water or another medium. In one possible embodiment, the fibers are in the form of a bed heaped up in the air stream. The formed fiber layer is first pre-compressed on a conveyor belt, on a movable sieve or a steel sieve, so that a loose fleece with low density and tear strength is created. The tensile strength should be high enough that the fleece can sag freely over a length of about 0.1 to 1 m without tearing. It should also withstand air pressure that can occur during manufacture. The fleece is then introduced into the nip of a pair of calender rolls which has a pattern of point or line-shaped projections on its surface. The point or line-shaped projections are preferably arranged such that they face each other and the fibers in these surface areas are pressed together under pressure in the range 150 to 600 MPa. The pressure exerted on the calender roll surfaces as a result of the opposing projections should be so high that embossing points are formed in these areas, in which the fibers form an intimate connection and cannot be detached without being destroyed. The fibrous web is preferably produced by a method and in a device such as that in the WO 99/25281 A1 is described.

In a preferred embodiment, the projections on the calender surfaces are arranged in such a way that an embossing pattern of punctiform or linear embossed areas is formed on the surface of the fibrous web.

In the production of the absorption material according to the present invention, binders such as are known from the prior art and are generally used can be practically dispensed with entirely.

The thickness of the absorption material according to the invention is preferably set so that the flat material can be used as absorbent in food packaging and in the hygiene sector and is preferably 0.2 to 4 mm, in particular 0.5 to 2 mm, measured in the non-embossed areas according to Edana method 30.5-99.

Depending on the application, the fibrous web according to the invention can have one or more further layers on its top and / or bottom, for example layers made of thin tissue material, nonwoven, breathable SMS, fabric and / or perforated two- or three-dimensional film. Nonwoven materials are textile-like materials that are made from long fibers and that are bonded together by chemical, mechanical, heat, or solution treatment. These are textile fabrics made of individual fibers that are permeable to liquids and are particularly suitable for use in the medical field, such as wound dressings. Materials from which the nonwoven materials or the perforated foils can be produced are preferably polyolefin foils, such as polyethylene or polypropylene foils or also natural material nonwovens. Other layers include laminates made of different materials, such as nonwoven and breathable film (BTBS films = breathable film textile backsheet), as are usually known for the production of the outside of incontinence products.

The other layers can already be applied during the production of the fibrous web according to the invention by applying the cellulose fill to a first layer and possibly covering it with a second layer. The layering of a first layer and cellulose fibers and, if necessary, a second layer can be introduced together into a calender. The two layers can be the same or different and can be adapted to the intended use.

In a further embodiment, further layers can be applied after leaving the calender.

The invention is illustrated by the following examples.

Examples

example 1

Commercial HT-CTMP with a brightness of 70% according to ISO 2470 is fibered and then after that in the WO 99/25281 described method, each with a layer of tissue on the top and Bottom processed into a fibrous web. The absorbency of the fibrous web obtained was investigated. The material was cut to a size of 10x10 cm.

Fibrous webs of different basis weights were produced and their absorption capacity compared to 0.9% NaCl solution without load (FSC), under load (BfR) and the retention (CRC) were examined. The results are shown in Table 1.

Absorbability without load (Free Swell Capacitv, FSC)

The FSC is determined analogously to the Edana test method 440.2-02. For this purpose, the sample pieces are weighed in a dry state (GTR1) and then welded into a spunbonded non-woven bag (approx. 150 mm * 150 mm) and weighed again (GTR2). The samples are then soaked together with the fleece bag in a bowl with 0.9% NaCl solution and left in the solution for 20 minutes. The liquid level must cover the sample at least 10 mm. The samples are then lifted out and placed on a sieve frame for 1 minute to drain. The samples are weighed again (GF). The evaluation takes place after $$\text{absorption}\left[\text{G}/\text{G}\right]=\left(\text{GF}-\text{GTR}2\right)/\text{GTR}1.$$

The measurement results are averaged and the standard deviation is determined.

Determination of retention (Centrifuge Retention Capacity = CRC)

CRC is the amount of liquid that a product absorbs when it is under a defined centrifugal force.

The CRC was determined analogously to the Edana test method 441.2-02 or ISO 17190-6: 2001. For this purpose, the samples are prepared as indicated above under the test description for FSC and soaked in 0.9% NaCI solution. The samples are then lifted out and dewatered for one minute in a centrifuge (Ø drum 340 mm, n = 2800 1 / minute). The samples are weighed again (measurement result GC).

The test is evaluated according to the following equation: $$\text{absorption}\left[\text{G}/\text{G}\right]=\left(\text{GC}-\text{GTR}2\right)/\text{GTR}1.$$

The measurement results are averaged and the standard deviation is determined.

Determination of the absorption capacity according to the BfR method

The absorption capacity according to the BfR method is carried out analogously to that in the 61st communication of the Federal Office for Risk Assessment (BfR), published in the Federal Health Gazette 04.2003. For this purpose, a test specimen cut from the absorbent insert is placed in a plastic cylinder with a sieve mesh base and loaded with a defined weight. The cylinder unit consisting of a cylinder with sieve cloth, absorbent insert, cover plate and weight is weighed and placed on a filter plate covered with filter paper and soaked with test liquid. After liquid has been absorbed over a defined period of time, the amount of liquid absorbed is determined by back-weighing the cylinder unit and specified as the suction capacity (g absorbed test liquid / cm ² suction insert) against the applied pressure. A 0.90% NaCl solution was used as the test liquid. In the experiments carried out here, the amount of absorption against a 0.9% NaCl solution and under a load of 1200 g / 100 cm ^{2 was} determined. Table 1 Location: 1 2 3 4 Tissue (g / m ² ) 18 18 18 18 Fiber (g / m ² ) 114 214 264 350 Tissue (g / m ² ) 18 18 18 18 Total (g / m ² ) 150 250 300 350 absorption FSC (g / g) 17.4 20.7 21.43 22.48 CRC (g / g) 1.68 1.65 1.64 1.58 BfR (g / g) 9.8 9.6 9.4 8.9

Example 2

The absorbency FSC of absorbent bodies from fluff pulp produced by the Kraft process was determined as in Example 1. Absorbent body made of fluff pulp basis weight dry (g / m ² ) After absorption of saline (0.9%) (g / m ² ) Absorption [g / g] FSC CRC g / g BfR g / g 60 465 7.8 1.1 5.85 70 660 9.4 1.2 4.9 120 1077 9.0 1.2 5.67 150 1502 10.0 156 1420 9.1 1.23 186 1487 8.0 210 1389 6.6 230 1320 5.7 1.17 4.52

Claims (13)

A process for producing an absorbent fibrous web, which comprises the process steps a) confusing laying of pulp fibers from CTMP in a gas stream on a base, b) pre-compressing the cellulose fibers to produce a loose fleece, c) inserting the fleece from step b) into the nip of a pair of calender rolls, the surfaces of the calender rolls each having projections with which the fibers from step b) are pressed together under pressure in the range between 150 to 600 MPa. Procedure according to Claim 1 , characterized , characterized in that the CTMP fibers are comminuted in a step preceding process step a) in a hammer mill, disc refiner or pin mill. Absorbent fibrous web from a bed of air-entrained cellulose fibers made of CTMP, obtained in an air stream, obtained by a process of Claims 1 or 2 , characterized in that the fibrous web has a free swell capacity (FSC) compared to a 0.9% NaCl solution of at least 16 g / g and an absorption capacity according to the BfR method of at least 6 g / g. Fibrous web after Claim 3 , characterized in that the fibrous web has a retention (CRC) of at least 1.3 g / g fibrous web. Fibrous web according to one of the Claims 3 or 4 , characterized in that the fibrous web has a free swell capacity (FSC) compared to a 0.9% NaCl solution at least 20 g / g and in particular at least 24 g / g. Fibrous web according to one of the Claims 3 to 5 , characterized in that the fibrous web has an absorption capacity under load determined by the BfR method of at least 8 g / g fibrous web. Fibrous web according to one of the Claims 3 to 6 , characterized in that the cellulose fibers used have a brightness of over 40%. Fibrous web according to one of the Claims 3 to 7 , characterized in that the fiber pulp has a bulk density between 5 and 300 g / cm ³ . Fibrous web according to one of the Claims 3 to 8th , characterized in that the fibrous web has a weight per unit area of 60 to 1500 g / m ² , preferably 90 to 900 g / m ² and in particular 120 to 700 g / m ² . Fibrous web according to one of the Claims 3 to 9 , characterized in that no polymeric suction boosters are included. Fibrous web according to one of the Claims 3 to 10 , characterized in that a web of textile, fleece-like or foil-like material is arranged on at least one of the surfaces. Fibrous web after Claim 11 , characterized in that the material is selected from tissue material, nonwoven, breathable SMS, tissue and / or perforated two or three-dimensional film. Use of the absorbent fibrous web according to one of the Claims 3 to 12 as an absorbent body in food packaging, in hygiene products and in medical products.